1. Field of the Invention
The present invention relates to a display apparatus for displaying characters or images, which display apparatus is used for a display unit of a computer, a view finder of a video camera, a television receiver, a navigation system, and the like. More particularly, the present invention relates to a liquid-crystal display apparatus for making a display by using two molecular orientation states shown by a chiral smectic liquid crystal.
2. Description of the Related Art
Hitherto, a liquid-crystal display device for displaying image information is well known, In such a device a liquid-crystal compound is filled between a scanning electrode group and an information electrode group showing a matrix electrode structure as matrix electrode means, and a number of pixels are formed. Above all, a ferroelectric chiral smectic liquid crystal having bistability and having quick response to an electric field is expected as a high-speed and storage-type display device, and is proposed in, for example, Japanese Patent Laid-Open No. 56-107216. Further, a number of driving methods of matrix-driving such a device have been proposed in Japanese Patent Laid-Open No. 56-107216, and others up to the present time.
FIGS. 13 and 14 show examples of conventional driving waveforms. In each figure, reference character A denotes a scanning selection signal, reference character B denotes a scanning non-selection signal, reference character C denotes an information signal when a bright display is made, and reference character D denotes an information signal when a dark display is made. Reference characters V.sub.1, V.sub.2, V.sub.3, V.sub.4 and V.sub.5 denote the voltage values of each pulse, and reference characters V.sub.c denotes a reference voltage value. Reference numeral 1H denotes one horizontal scanning period. If the number of scanning lines is n, and the scanning period of all the scanning lines is 1F, the product of the 1H and n becomes 1F.
In the device using a conventional liquid crystal, if the device is left for a long period of time in one of the molecular orientation (stable) states, its characteristics as a display device may vary due to the interaction on the interface between the substrate and the liquid crystal. In the driving waveform (a first conventional waveform) shown in FIG. 13, at least information signals shown at C and D of FIG. 13 are constantly fed to the liquid crystal for the purpose of speeding up the frame frequency. When the continuous width pulse of .DELTA.T is fed in this way, a phenomenon was found to likely occur when all of the pixels are displayed bright or dark in which the fluctuations of the liquid crystal molecules during the scanning non-selection become large, a part of the display is reversed, and a satisfactory display state cannot be maintained.
As compared with this, in order to secure a range (driving margin) of driving conditions in which a satisfactory display can be made, the driving waveform (a second waveform) shown in FIG. 14 was invented first. According to this waveform, the provision of a pause period of 1/2 .DELTA.T at the beginning of the selection and non-selection signals within the 1H duration shown at C and D of FIG. 14 causes the fluctuation of the liquid crystal molecules to be suppressed and causes the driving margin to widen.
However, in this liquid-crystal device, electromagnetic induction occurs in the scanning signal electrode due to the information signal, and a delayed, overshot composite waveform is applied. At this time, the contrast varies, causing the image display quality to deteriorate. Further, when driving continues for a long period of time, the driving margin may deteriorate, in particular, crosstalk may occur. In such points, it has become clear that there is still room for improvement in the waveform of FIG. 2.